Dehydrocyclization of paraffins

ABSTRACT

PROCESS OF DEHYDROCYCLIZING C6-C10 PARAFFINS USING A SODIUM ZEOLITE X OR SODIUM ZEOLITE Y, WHICH ZEOLITE HAS BEEN ION EXCHARGED WITH FROM 0.10 TO 1.2 WEIGHT PERCENT PLATINUM, THE CATALYST CALCINED AND THE PLATINUM THEN REDUCED WITH HYDROGEN TO THE FREE METAL. IN AN ESPECIALLY PREFERRED ASPECT OF THE INVENTION, THE CATALYST IS GIVEN A FINAL ION EXCHANGE WITH A SODIUM SALT SUCH AS SODIUM BICARBONATE. THE DEHYDROCYCLIZATION REACTION IS CARRIED OUT AT FROM 500-560*C. AND PREFERABLY FROM 510 TO 555*C. USING A PARTIAL PRESSURE OF HYDROGEN OF FROM 10 TO 300 P.S.I.G. AND PREFERABLY 50 TO 200 P.S.I.G. TO FORM BENZENE AND ALKYLBENZENES.

United States Patent 3,775,502 DEHYDROCYCLIZATION 0F PARAFFINS Masayoshi Oishi, Wilmington, Del., assignor to Sun Research and Development Co., Philadelphia, Pa. No Drawing. Filed May 8, 1972, Ser. No 250,991 Int. Cl. C07c 3/02; 010g 35/08 US. Cl. 260-6735 7 Claims ABSTRACT OF THE DISCLOSURE Process of dehydrocyclizing C C paratiins using a sodium zeolite X or sodium zeolite Y, which zeolite has been ion exchanged with from 0.10 to 1.2 weight percent platinum, the catalyst calcined and the platinum then reduced with hydrogen to the free metal. In an especially preferred aspect of the invention, the catalyst is given a final ion exchange with a sodium salt such as sodium bicarbonate. The dehydrocyclization reaction is carried out at from 500 to 560 C. and preferably from 510 to 555 C. using a partial pressure of hydrogen of from 10 to 300 p.s.i.g. and preferably 50 to 200 p.s.i.g. to form benzene andalkylbenzenes.

BACKGROUND OF THE INVENTION In the processing of petroleum into gasoline, it is known that normal paraflins are undesirable gasoline components because of their very low octane ratings. Generally modern refining technology calls for reforming the straight run gasoline fraction using a supported noble metal catalyst. Generally this reforming is carried out at 450 to 500 p.s.i. and converts naphthenes into aromatics and normal paraffins into isoparaflins. It is also known that the normal parafiins can be removed from the straight run gasoline by means of mole sieves. This is not generally carried out commercially because of the expense involved and the extremely low value of one of the products, namely, the normal paraflins. The present invention is directed to upgrading these normal paraflins into high octane gasoline components particularly aromatics. These aromatics has a wide variety of other well known uses such as solvents, etc.

SUMMARY OF THE INVENTION The present invention relates to the dehydrocyclization of parafiins and particularly normal paraflins containing from 6 to 10 carbon atoms to form aromatic compounds.

The catalyst used in the present invention is a zeolite which has been ion exchanged with platinum and then had the platinum reduced to the free metal state. This catalyst has been found to be superior for catalyzing dehydrocyclization of paraflins to similar catalyst which have been prepared by simply impregnating the zeolite with platinum. The zeolites used in the present invention are sodium zeolite X and sodium zeolite Y. Zeolite X has the typical formula:

ss[( 2)se( 2)1os] 2 Zeolite Y has the typical formula:

a[( 2)56( 2)1ss] 264H20 A further description of these zeolites may be found in Crystalline Molecular Sieves by D.W. Breck, Journal of Chem, 41, 678-689 (1964).

Zeolite X is preferred because zeolite Y has a greater tendency to coke up during the dehydrocyclization reaction.

DESCRIPTION After the desired zeolite is obtained, it is ion exchanged with from 0.10 to 1.2 Weight percent platinum. Below about 0.10 percent platinum, the catalyst is not sufficient- "Ice ly active. Above about 1.2 percent platinum, insufficient improvement in catalyst activity is obtained to warrant more use of expensive platinum. The zeolite is ion exchanged with platinum by treatment with an aqueous solution of both a sodium salt of a strong acid and a soluble platinum salt at a moderate temperature for several hours. Generally this treatment is carried out at from 25 to C. for a period of from 1 to 24 hours. The ion exchange solution generally will contain from 1X 10- to 0.1 molar platinum and from 1 to 10 molar sodium. The pH of the ion exchange solution ordinarily will be from 7 to 9. The catalyst is then washed thoroughly with a solvent such as water to remove the salt residue and is then dried and ground. The catalyst is then calcined by heating at from 400 to 650 C. in an oxygen-containing atmosphere such as air or pure oxygen for from 1 to 6 hours. Then the platinum is reduced to the free metal by treatment with flowing hydrogen for 1 to 4 hours at 350 to 550 C. The resulting catalyst has improved activity as compared with a similar catalyst which has been simply impregnated with platinum.

In a typical preparation, a large quantity of zeolite X such as g. is air dried in an oven overnight at C. A ten gram sample of the dried zeolite X is added to a flask containing 200 ml. of distilled water and 61.4 g. of NaCl. This mixture is stirred for 15 minutes while the temperature is maintained at 60 C. A solution of 0.2 g. of Pt(NH Cl 'H O in 100 ml. of distilled water is added dropwise to the contents of the flask. The resulting slurry is stirred overnight while being maintained at 60 C. The resulting mixture is filtered and the resulting cakelike catalyst is Washed thoroughly with distilled water until it is substantially free of chlorine. The catalyst is dried for 2 hours at 100 C. in an oven after which it is hand ground until it passes through a #40 mesh screen (U.S. Sieve Series). The catalyst is then calcined at 500 C. with 10 cc./min. of air flowing. The final temperature is reached in about two hours. The catalyst is reduced with hydrogen in the reactor before the runs.

In an especially preferred embodiment of the present invention, the catalyst is given a final treatment with an aqueous sodium bicarbonate salt. This serves to convert the H+ zeolite sites, which were created when the platinum was reduced to the free state, back to Na zeolite sites, providing a catalyst substantially free of acid zeolite sites. Generally, this treatment should be done with a sodium salt solution having pH of greater than 8. The solution should be diluted and generally will be from 0.01 to 24 hours at from 25 to 80 C. The anionic position of the sodium salt should be one which is readily removable from the zeolite. Thus sodium carbonate, sodium bicarbonate are preferred for this use. A preparation of such a catalyst involves treating ten grams of the platinum ion exchanged and reduced X-type zeolite described above with 100 ml. of a 0.1 N NaHCO aqueous solution for 12 hours at 60 C.

The catalysts of the present invention contain the platinum in substantially the mono molecular free metal state due to each platinum ion having been associated with an individual pt zeolite site and then reduced to the Pt H+Z state wherein individual molecules of free platinum metal are physically located adjacent individual H+Z sites. The platinum dispersion of the catalyst used in Example 1 has been found to be 94.3% Preferably the catalysts of the present invention have platinum dispersions of at least 50% Due to the high dispersion of platinum in the present catalysts, the presence of chlorine which is often used to aid in the dispersion of the platinum is unnecessary and in fact undesirable due to the otherwise deleterious effect of chlorine on the dehydrocyclization activity of the catalyst.

Thus the catalyst should contain less than 0.20 weight percent chlorine.

The dehydrocyclization is generally carried out using a liquid hourly space velocity as based on feed of from 0.1 to 40 and preferably from 2 to 15. The dehydrocyefiiuent from this injection is not analyzed. A 2 microliter charge of the material being dehydrocyclized is then injected through the septum and the resultant efiluent is programmed through a previously calibrated gas chromatograph. The definitions of selectivity reported in clization is carried out at from 500 to 560 C. and prefthe table are: erably from 510 to 550 C. Above 555 C. and especially above 560 C. the amount of cracking taking place percent cychzatlon starts to increase rapidly. Below 500 C. the amount of =aromatlcs percent)+naphthencsxloo conversion of the paraffin is too low. The amount of cy- 0011119151011 P clization as opposed to the amount of isomerization inpercent i i ti creases conslderably abqut 9 total isomers of same number The dehydrocychzation 1s carried out under moderate f b t t r t) pressure expressed herein in terms of partial pressure of :W X 100 hydrogen in the reactor. The partial pressure of hydrogen converslon percent) generally is from 10 to 300 p.s.i.g. with from 50 to 200 percent cracking p.s.i.g. being the preferred range. Below 50 p.s.i.g. and total of lesser numbered carbon especially below 10 p.s.1.g. coking of the catalyst beatoms (wt. percent) comes too rapid to be economical. As the pressure in- X100 conversion (wt. percent) creases above 200 p.s.i.g. and especially above 300 p.s.i.g., the cracking and isomerization reaction become favored The two catalysts used in the examples are prepared instead of the dehydrocyclization reaction. in accordance with the two typical catalyst preparations Suitable paraflinic starting materials contain 6 to 10 described above. The hydrogen reduction of the catalyst carbon atoms. Any parafiin containing from 6 to 10 was carried out for 2 hours. In all the examples, the carbon atoms is suitable. Generally, the normal paraffins ion exchange solution contained 0.2 g. Pt(NH Cl -H O are preferred because due to their low octane numbers, in 100 ml. of the salt solution indicated and the treatthey can be improved more than the branched paraffins ment was carried out at 60 C. for 16 hours.

TABLE Dehydrocycllzation cl n-Heptane Selectivity, percent Pres- Converycl./ Exam- Temp., sure, sion, Cycll- Isomer- Crackcrackple Catalyst C. p.s.i.g. percent zation lzation ing ing Remarks 1 0.25% Pt/NaX, 0.07% Cl (Pt ion ex- 510 150 23.9 21.4 26.4 52.2 0.41 Get. reduced at 500 C. with cc changed in 5.25M NaCl aqueous Hz/Dllll. solution).

510 100 27. 0 38. 7 23.0 38. 3 1.01 Do. 510 50 41. 9 53. 8 22. 0 24. 2 2. 26 D0. 510 150 33.9 29.2 27.4 43.4 0.67 Get. reduced at 500 C. with 250 cc.

H /min. 510 100 44. 1 39. 3 30. 1 30. 6 1. 31 Do. 6.. ..d0 510 50 58.7 60.2 21. 2 18.6 3.24 D0. 7 0.30% Pt/NaX, 0.04% 01 (Pt ion ex- 510 150 29.2 19.8 33.1 47. 1 0.42 Get. reduced at 500 C. with 50 cc.

changed in 2.63M N aCl). /min. 8 do 510 100 33.6 30. 9 31. 8 37. 4 0.83 Do. 9 do 510 50 52. 2 52.0 24. 8 23.2 2. 24 Do. 10..." 0.30% Pt/NaX, 0.04% Cl (Pt ion 510 150 67.5 23.0 24.4 52.6 0.44 Cat. reduced at 500 C. with 250 cc.

exchanged in 2 63M NaCl) H; min. 11 do 510 100 67. 0 40.0 26. 3 33. 7 1.10 Do. 12 do 510 50 77.6 53.6 18.8 27.6 1.94 Do. 13 0.27% Pt/NaX, 0.02% 01 (Pt ion ex- 500 100 26.5 44.2 34.2 21.7 2.04 Cat. reduced at 500 C. with 50 cc. changed in 5.25M NaCl). Hz/min. post treat with 0.1 N

NaHCOa 520 100 52. 7 51. 1 31. 8 17. 2 2. 97 D0. 550 100 92.0 63. 0 8. 2 28.8 2.10 D0. 500 100 58.8 22.5 42.0 35.5 0.64 0%.]reduced at 500 C. with 50 cc.

1 111111. 520 100 77. 1 37. 8 25. 4 36.8 1. 03 Do. 550 100 99. 3 60. 7 1. 3 38.0 1. D0.

which have higher octane numbers. Ordinarily the feed stream will be the normal hydrocarbons removed by denormalization of a C -C petroleum stream which would consist essentially of C -C normal hydrocarbons.

In Examples 1 to 18 a pulse microreactor is used. This reactor is a stainless steel tube about 200 mm. long and having an inside diameter of 4 mm. The inside of the tube contains pyrex wool retainers which keep the catalyst in place. In each of the examples, the tube is packed with 0.125 g. of catalyst. The tube is fitted in a brass mounting sleeve which contains a thermocouple in a well. The brass sleeve in turn mounted in a four-inch electric furnace operated on 115 volts and controlled by a 7.5 amp powerstat. The top of the tube is fitted with a silicone rubber septum mounted in a septum holder and a carrier gas inlet. The carrier gas is deoxygenated by hydrogen passed through the system at a rate of about 50 cc. per minute under the pressure indicated in the particular example being reported. The catalyst is preconditioned by injecting a 30 microliter pulse of the n-heptane which is being dehydrocyclized. The reactor The invention claimed is:

1. A process of dehydrocyclizing at least One normal paraffin containing from 6 to 10 carbon atoms comprising contacting a feed stream consisting essentially of normal parafiins with a catalyst which is a zeolite selected from the class consisting of sodium zeolite X and sodium zeolite Y wherein from 0.10 to 1.2 weight percent as based on said zeolite of platinum ions have been ion exchanged with the sodium ions, the catalyst calcined and the paltinum then reduced with hydrogen to the free metal state, at from 500 C. to 560 C., at a liquid hourly space velocity of from 0.1 to 40 under a hydrogen partial pressure of from 10 to 300 p.s.i.g., whereby at least a portion of said normal paraffin is dehydrocyclized.

2. The process of claim 1 wherein the catalyst is derived from zeolite X.

3. The process of claim 2 wherein the hydrogen partial pressure is from about 50 p.s.i.g. to 200 p.s.i.g.

4. The process of claim 3 wherein the temperature is from 510 C. to 555 C.

5. The process of claim 4 wherein the liquid hourly space velocity is from 2 to 15.

6. The process of claim 5 wherein the paraflin starting material is a hydrocarbon feed stream consisting essentially of normal paraflins containing from 6 to 10 carbon atoms.

7. The process of claim 6 wherein catalyst is substantially free of acid zeolite sites.

References Cited UNITED STATES PATENTS 2,971,904 2/ 1961 Gladrow et a1. 260-673 5 DELBERT E. GANTZ, Primary Examiner J. D. M. NELSON, Assistant Examiner US. Cl. X.R. 

